Method for making resistors



May 12, 1942. e. e. HERRICK ETAL METHOD FOR MAKING RESISTORS Filed Dec. 5, 1939 INVENTORS GEORGE G. hmzw/cK //u 1/ IV. 2? 2; Q d W ATTORNEY.

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VPatented May 12, 1942 METHOD FOR MAKING RESISTORS George G. Herrick and Hugh N. Veley, St. Marys, Pa., assignors to Speer Resistor Corporation, a corporation of Pennsylvania Application December 5, 1939, Serial No. 307,555

3 Claims. (Cl. 18-59) In certain fields of use, such as in radio circuits, high resistance units with insulation coverings or shells are required. It has been the practice in the past to make the unit and insulation shell in separate steps. For example, the resistance unit, 01' resistor as it is usually called, has been made of Various proportions of owdered carbon, clay, asbestos, and other materials'm'fized with a binder such as a phenol condensation product, pitch, or other hydrocarbon. The amount and character of the materials used, of course, depended upon the value of the resistance desired. The resistor material was then compressed in a mold to the desired shape. The shaped resistor was next baked at the desired temperature to set the binder or otherwise firmly join the ingredients together.

A coating of some protecting insulation material was then molded under pressure around the resistor and the two were heated to form the insulation material into a hard shell.

It is the object of this invention to avoid the separate steps of pressure molding and heating of the resistor and shell as used in the prior art and to form the resistor and insulation shell with practically one application of heat.

Another object of the invention is to start the formation of the resistor and its insulating covering while both are in the substantially uncompressed condition so that subsequently applied pressure will cause the shell to make a more intimate contact with the resistor and thereby facilitate the radiation of heat when the finished resistor is in use.

Other objects will appear in the following description, reference being had to the drawing in which:

Fig. 1 is a sectional view of a mold, illustrating one step in the process of forming a resistor.

Fig. 2 illustrates a second step in the process.

Fig. 3 illustrates a further step in the process of forming the resistor.

Fig. 4 illustrates the final step in the molding process.

Fig. 5 is a view of the completed resistor and terminal connections.

Fig. 6 is an enlarged view of a section of the resistor, showing how the resistor material interlocks with the shell, the interlocking being exaggerated somewhat to aid in an understanding of the principle involved.

Since our invention is not concerned with the materials of the shell and the resistor or the particular proportions, definite materials and proportions need not be given.

Referring to Figure 1, the mold table 2 is placed over the ram l in such a position that pin 3 extends coaxially with the mold opening. Sleeve 4 surrounds the pin 3, one end resting on the ram I and the other projects into the mold 2 a slight distance, as shown. The powdered insulation material 6, such as a phenol condensation product, is then introduced into the annular opening inside the mold 2 around the pin 3. A plate 5 of appropriate thickness may serve as a gauge in this filling process, the plate being of sufiicient thickness to provide for the correct amount of compression when the shell material is filled into the mold flush with the top of the plate. Pressure is then applied to the top ram 1 and it is brought down until the bottom of the sleeve 8 is substantially flush with the top surface of the table 2, as indicated in Figure 2. During this operation, pressure may also be applied to the ram I if desired. The relative movement of the two rams will, of course, determine the amount of compression.

Rams l and 1 are then withdrawn and pin 3 is pushed out while sleeves 4 and 8 are in the mold to prevent damage to the slightly compressed shell. Sleeves 4 and 8 are next withdrawn leaving the shell in the mold just sufiiciently compacted to keep its form while the next step in the process is started.

The mold is then placed over the ram l with another sleeve or piston 9 in position, as shown in Figure 3. This piston contains a terminal l0 held therein so that the enlarged end H extends somewhat into the central channel of the shell 6. In this position the piston 9 extends suificiently into the mold opening to close the mold at the lower end. Powdered resistance material of whatever composition desired is then poured into the central channel in shell 6 until it is flush with the upper surface of the mold table 2. A second piston I2 is then placed over the mold under the ram 1. The piston I2 also has a central opening containing a terminal l3. After bringing the piston l2 into position over the upper opening of the mold, the upset end l4 of the terminal is pressed into the loose resistance material.

Sufiicient pressure is next applied to the upper ram 1, and also the lower one if desired, to compress the shell and resistance material to the full extent necessary. The head M of the terminal will move properly with the resistance material as it is compressed since the terminal can move in the channel in the sleeves 9, l2 or buckle therein as the case may be. This last step in the molding process is indicated in Figure 4. It will be noted that the shell 6 has been compressed around the resistor until the insulation material completely surrounds its end.

After the resistor and shell is thus completely compressed, the rams and pistons are withdrawn and the resistor is forced out in any way.

The resistor, after being completed with its insulation shell, will appear as in Figure 5. It may then be placed in any suitable oven and baked to the desired temperature to set the binder in the resistor and polymerize or otherwise complete the formation of the shell by the application of heat. The heating may be carried out in any way well known in the art and a descrip tion of this is unnecessary.

It has been found that a resistor formed simultaneously with the shell by one application of high pressure radiates heat to a better extent than an identical resistor with an identical shell formed in two applications of high pressure. This appears to be due to the fact that the particles of the powdered resistancematerial are forced into and interlock with the material of the shell, which at the time of the compression of the resistance material is only slightly compressed. This is indicated in Figure 6. It would be immaterial whether the material of the shell is forced into the resistance material or vice versa. In either case, sufliciently better contact between the two materials is obtained to cause the heat developed in the resistor in use to be more quickly radiated through the shell. Simultaneous heating of shell and resistance materials may also produce a more intimate contact between the two.

The apparatus shown in the drawing is, in general, symbolic only and it is to be understood that commercial molding need not be carried out in the more or less hand method described. Such hand method, of course, would be satisfactory for forming the resistance material with its surrounding shell, but in quantity production the apparatus may be differently arranged.

Having described our invention, what we claim is:

1. The process of making a resistor with a protecting shell which comprises in lightly compressing plastic insulation material into the form of a hollow cylinder, filling the bore in said cylinder with resistance material, inserting terminals in the ends of the resistance material, compressing the cylinder over the ends of the resistance material and around the terminals and continuing the compressing of the cylinder and the contained resistance material until both are compacted to the desired density.

2. The process of making a resistor with a protecting shell which comprises in lightly compressing a plastic insulation material inside a mold around a pin to form a temporary shell, removing the pin, filling the opening in the shell with plastic resistance material, inserting terminals in the ends of the resistance material, compressing the ends of the shell over the ends of the resistance material and around the terminals and continuing the compressing of the insulation and resistance materials until both are compacted to the desired density.

3. The process of making a resistor with a protecting shell which comprises lightly compressing plastic insulation material into the form of a hollow cyinder, filling the bore in said cylinder with resistance material, inserting terminals in the ends of the resistance materiaL'forcing the ends of said cylinder inwardly and compressing them over the ends of the resistance material and around the terminals, and continuing the compressing of the cylinder and the contained resistance material until both are compacted to the desired density.

GEORGE G. HERRICK. I HUGH N. VELEY. 

